1. Field of the Invention
The present invention relates to an electronic device such as a semiconductor device or the like and a method for manufacturing such an electronic device, specifically to an electronic device and a manufacturing method therefor in which a molding is provided with a protection layer applied over the entire body of the electronic device.
2. Description of the Prior Art
Conventionally, an electronic device such as a semiconductor device or the like is wirebonded and a molding material is applied over the entire body of the electronic device.
Generally, in a plastic molding package, water which reduces the reliability of the electronic device enters the molding from external sources, and has a tendency to collect on the rear or under side of the die of the lead frame. Then this moisture vaporizes quickly when the package is soldered (this generally involves immersion in molten solder at 260xc2x0 C. for 3 to sec). As a result, the molding which is softened by this heating swells, so that cracks or bulging are induced in the molding itself.
A conventional semiconductor device as shown in FIG. 1 comprises a lead 35 and a die 35xe2x80x2, an IC chip 28 die-attached to the die 35xe2x80x2 and a molding 41.
The frame die 35xe2x80x2 is made of metal such as copper, xe2x80x9c42 Alloyxe2x80x9d or the like, on the surfaces, specifically on the under or reverse side, of which a low class oxide 32 is inclined to be formed during heat treatment at 100xc2x0 C. to 350xc2x0 C. when the electronic part 28 is die-attached to the die 35xe2x80x2 through a paste layer 24.
For this reason, if the molding process is performed using an organic resin to form a molding 41 immediately after the die-attaching, an extremely easily-peeled oxide layer 32 remains between the molding 41 and the copper or xe2x80x9c42 Alloyxe2x80x9d. When this electronic device is stored for a long period, the moisture from the air is absorbed by the molding 41 and the moisture is accumulated in the vicinity of the oxide layer 32. For this reason, the electronic device is unable to withstand the sudden thermal shock that occurs when solder is subsequently applied for 3 to 10 sec at 260xc2x0 C., and cracks 33, 33xe2x80x2 are produced in the molding 41 around the periphery of the die 35xe2x80x2. In addition, the moisture collected on the rear side of the die 35xe2x80x2 is converted to steam and a void 42 occurs at that point, so that swelling 41xe2x80x2 (the phenomenon of swelling occurs because the water in the vicinity of the die 35xe2x80x2 turns to gas as a result of the temperature elevation when solder is applied to the molding 41 on the rear side of the die 35xe2x80x2) occurs on the under or rear side of the molding 41. Then, for a long time use after it is mounted on a printed-circuit board (PCB), the entry of water and impurities at the location of the cracks induces a deterioration in the characteristics and reliability of the semiconductor device.
In addition, in the prior art, the molding 41 is made from an insulating material of organic resin with a high specific resistance of 1xc3x971017 xcexa9cm or greater, therefore, at time of assembling using surface mount technology (SMT), static electricity accumulates on the surface of this insulated molding material through the contact with a jig surface or during storage. When this organic resin is thick, the electric field strength in the mold is relatively small, and the electrostatic discharge damage of the electronic parts does not often occur. However, when the thickness of the molding material is 1.5 mm or less, the strength of the electric field of the static electricity becomes relatively large, and, it can not be ignored from the aspect of guaranteeing the reliability of the electronic parts.
An object of the present invention is to provide, with due consideration to the drawbacks of such conventional devices, an electronic device in which the decrease in reliability is prevented.
Another object of the present invention is to provide a reliable device wherein an electronic device such as a semiconductor device or the like is wirebonded and molding is applied over the entire body of the electronic device.
Another object of the present invention is to use a non-product gas (a gas which does not decompose to form a film of a solid reaction product) for the plasma process to provide a densified layer, so that the surface of the molding modified into the densified layer, or a densified layer is formed on the surface of the molding.
Another object of the present invention is to prevent the development of cracking and swelling by improving the adherence of the die to the molding or protective film which adhere to the die.
Another object of the present invention is to provide a molding process which is carried out on the entire body of the device has been wirebonded, so that the molding operation provides a densified layer on the surface in order to prevent entry of moisture from external sources into this molding.
In the present invention, there is no protective film formation (final coating) at the wafer level to prevent deterioration caused by water permeating the molding, but instead after the molding process (molding process by an organic resin), this film is provided on the outside of the electronic parts, by a plasma process using inert gas such as argon or a fluorinated gas over the molding after the molding process, or by using silicon nitride, xe2x80x9cDiamond-Like Carbonxe2x80x9d (DLC, referred to as so because it is carbon with the same sp3 bond as a diamond), or the like over the molding after the molding process.
These objects are achieved in the present invention by the provision of a densified layer after completion of the molding process, which prevents the permeation of moisture into the moldings.
Used as the means for providing this densified layer in the present invention are a method of plasma-hardening the organic resin molding in the vicinity of the surface by means of an argon or the like plasma process conducted on the entire body of the device, and plasma CVD (chemical vapor deposition) process by which the coating of a silicon nitride film or a DLC film acting as a protective film is formed to prevent moisture permeation into this surface.
In the present invention, an even more reliable electronic device can be fabricated using a plasma process, by covering the entire lead frame and chip with silicon nitride, before forming the molding.
Still another object of the present invention is to provide, with due consideration to the drawbacks of the conventional DIPs (dual in-line packages), an electronic device in which a decrease in reliability from a localized breakdown in the electronic parts because of static electricity and the occurrence of cracks is prevented.
Another object of the present invention is to provide a manufacturing method for forming, on the surface of the molding, a carbonaceous film of carbon or of a substance including carbon as the main ingredient in order to prevent the breakdown of the inner sections of the electronic parts, and to prevent the permeation of external moisture into the interior of the molding material.
These objects are achieved in the present invention by the provision of a carbonaceous film of carbon or of a substance including carbon as the main ingredient, formed on the surface of the molding after completion of the molding process.
For these purposes, the present invention uses a CVD method, utilizing a carbon compound gas, in the application of a film of carbon, or of a material of which carbon is the main ingredient, which has good heat transfer capabilities and which has superior adhesion to the organic resin molding (referred to as DLC).
In the present invention, a carbonaceous film of carbon or of a substance including carbon as the main ingredient, which has good adherence to the organic resin, is formed to a thickness of 0.05 to 5 xcexcm, or preferably of a thickness of 0.1 to 1 xcexcm. In order to form this film, a vacuum is first applied to the electronic device covered with molding to draw off the moisture in the molding material. The surface then has weak insulating characteristics as a countermeasure against static electricity. To prevent permeation of water from the exterior, the carbonaceous film (DLC film) is formed as a protective film, using the vacuum along with the plasma CVD method for forming a coating from the sputtering effect. The carbonaceous film applied onto the surface of the molding has a specific electric resistance between 1xc3x97106 and 5xc3x971013 xcexa9cm.